In ceramic electronic components such as multilayer ceramic capacitors, external electrodes are often plated with tin to improve their solderability. The external electrodes are generally electroplated in a sulfuric acid bath, a sulfamic acid bath, an alkanesulfonate bath, an alkanolsulfonate bath, a fluoroboric acid bath or a phenolsulfonic acid bath.
However, the sulfamic acid bath or the alkanesulfonate bath may cause elution of barium in the bath for barium-containing ceramics such as barium titanate ceramics. The elution of barium results in erosion of the ceramics, thereby often reducing the insulation resistance of the ceramics.
In the sulfuric acid bath, tin ions coexist with sulfate ions. Thus, the sulfuric acid bath causes little elution of barium even for the barium-containing ceramics, and therefore hardly reduces the insulation resistance of the ceramics. However, ceramic components may adhere to each other during plating.
To prevent this adhesion, Patent Document 1 proposes a method of tin plating in a bath that contains tin ions, sulfate ions and ions of at least one acid selected from the group consisting of sulfamic acid, alkanesulfonic acids, alkanolsulfonic acids, fluoroboric acid and phenolsulfonic acid at a tin ion concentration of 0.008-0.84 mol/L and a sulfate ion concentration of 0.02-0.31 mol/L at a pH of 4.1-6.0.
Patent Document 1 states that use of the tin plating bath containing these particular components can reduce the elution of barium from the barium-containing ceramics and prevent electronic components from adhering to each other by plating.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-107693